The recently synthesized enantiomers of l-(l-phenylcyclohexyl)-3-methyl-piperidine (PCMP) were used to detect stereospecificity of displacement of high affinity [3H]-PCP in rat olefactory bulk slices. Long acting and essentially irreversible binding of 2-nitro and 2,8-dinitroimipramine to high affinity binding sites on human platelets was observed suggesting that these compounds will be of value in isolation and purification of these binding sites. Antagonism of enkephalin-induced changes in spontaneous cell firing in vivo by (+)-and (-)-naloxone was studied.